The separation of resin into its
component parts, rosin and turpentine, involves two basic operations: cleaning and
distillation. Cleaning is necessary to remove all extraneous material from the resin, both
solid and soluble. This includes forest debris such as bark, pine needles and insects,
which may have fallen into the cup during its period on the tree, and which require
removal by filtration. Water-soluble impurities carried into the cup by rain water are
removed by washing the filtered resin with water. The approximate composition of crude
resin, as it is received at the plant for processing, is 70% rosin, 15% turpentine and 15%
debris and water. Small amounts of iron produced by the corrosive action of excess
sulphuric acid on galvanized iron guttering and cups may also contaminate the resin. As
the presence of iron would lead to a darker, lower-grade rosin, it is removed by adding
oxalic acid prior to filtration. Iron contamination has become less of a problem as the
use of acid paste rather than spray has become more widely adopted. The use of cups made
of plastic or other non-ferrous material eliminates the risk of iron contamination from
this source.

The cleaned resin is then ready to
be distilled, or, to be precise, steam-distilled; the older type of direct-fired still has
given way, almost universally, to a still in which steam is used both to heat the resin
and to facilitate the distillation by co-distilling with the turpentine vapours. Designs
of equipment, and the procedures followed, vary somewhat between producing countries. The
Olustee process, developed and used in the United States and adopted elsewhere, is
described first. The methodology is well documented, and since the differences between
this and any other system of processing are likely to be matters of detail rather than
principle, a description of the process serves as a useful guide to any prospective
processor of crude resin. The final design of plant can be tailored to suit local
preferences and requirements in terms of scale. A description is then given of Portuguese
methods which are based on the same principles as the Olustee process, but which differ in
the layout of equipment and the relative capacity of some of the units. Processing methods
used in other producing countries are not described. To a greater or lesser degree they
all follow the same basic principles, namely, filtration of the hot, diluted resin,
usually including a washing stage, and steam-distillation.

The scheme of processing is
illustrated in Figure 2. Barrels of resin arriving at the plant are immediately weighed
and upturned over an iron grill covering a large concrete or mild steel dump vat. The
barrels are placed over steam outlets to remove the last of the adhering semisolid resin.
'Scrape', the solidified resin which is taken off the face of the tree at the end of the
season and which yields a poorer quality rosin, is emptied into a separate compartment for
separate processing.

Figure 2. Scheme of resin
processing in the United States of America

Source: Based on McConnell (1963)

In order to facilitate the flow from
one unit to another, the resin has to be diluted with turpentine and heated. As well as
making the resin more fluid, dilution lowers its specific gravity, so that in the later
washing stage it will form a two-phase system water more readily. The resin is transferred
first from the dump vat to a blow-case, and then from the blow-case to a melter, by the
use of steam pressure. Filter aid (diatomaceous earth, 0.5-0.6 kg/tonne of resin) and
oxalic acid (0.6-1.2 kg/tonne) are added at either of the two units. Turpentine (from a
previous distillation) is added to bring the turpentine content of the resin to between
30% and 40% the precise amount added depends on whether good quality resin or 'scrape' is
being processed. The temperature inside the melter is raised to 85-100°C by steam, the
exact temperature again being dependent on the quality of the resin. Steam pressure is
then used to force the hot resin first through a metal screen at the bottom of the melter
to remove the larger sized solid matter, and then through a filter to remove all remaining
solids. The filter is of the horizontal or vertical plate type and consists of about 12
plates backed with filter paper or cloth; filtration is assisted by the filter aid added
previously. The resin passes directly from the filter to the bottom of a wash tank
containing hot water. Each tank holds 1500-2000 litres of water which is sufficient for
washing up to 20000 litres of resin (about seven charges from the melter). After washing,
the mixture is allowed to settle for at least 4 hours and preferably overnight. The bottom
aqueous layer is then run off to waste, an intermediate layer of unbroken emulsion
('muck') is run off to be returned to the low grade dump vat for reprocessing, and the top
layer, which consists of washed resin, is drained and pumped to a charge tank in
preparation for distillation.*

* Simple batch, rather than
continuous or vacuum distillation, is most commonly used and is described here, although
the other methods offer some advantages in terms of product quality and steam consumption
if there is sufficient throughput of resin to justify their use.

The still is filled with resin from
the charge tank. The temperature is then raised by means of steam coils to about 110°C at
which point live steam is gradually introduced through sparger valves. As the temperature
continues to rise, distillation proceeds and the sparger steam inflow is increased until,
at the end of the distillation, the temperature has reached 160-170°C. The rate of
increase in temperature, and therefore the time taken for the distillation, is dependent
on the steam pressure used; the higher the pressure within the range 8.8-10.5 kg/cm2
(125-150 psi), the faster the distillation. For still capacities of about 4-5 tonnes,
distillation times vary between 90 and 150 minutes. If the steam pressure is too low, it
will be more difficult to remove the last of the turpentine (particularly if there are
appreciable amounts of high-boiling components) and there will be an inordinately long
residence time for the hot rosin in the still; both these factors have an adverse effect
on the quality of the rosin. The turpentine and steam vapours pass through an entrainment
trap to remove any entrained resin and then condense in a water-cooled condenser.
Completion of distillation is indicated by a minimal level of turpentine in the distillate
(which, by experience, is found to correspond to a particular temperature). A small
proportion of the turpentine coming over at the beginning and end of the distillation may
be collected separately as slightly lower-quality turpentine, and used for diluting the
next batch of resin at the melter. Otherwise, there is no fractionation.

The water-turpentine distillate is
led immediately to a separating tank; the upper turpentine layer overflows and passes
first down to the base of the dehydrator and then upwards through a bed of rock salt to
remove all traces of water. The dry turpentine is then fed to holding tanks for subsequent
storage in bulk or in galvanized steel drums. The hot rosin from the body of the still is
discharged from the bottom into suitable containers which are set aside for the rosin to
cool and solidify.

Yields of rosin and turpentine
obtained by US producers were about 700 kg and 160 litres (140 kg), respectively, from one
tonne of resin. 'Scrape' yields less turpentine than normal resin. Specifications for both
products are given in Appendix 2. The general appearance of the rosin should be hard,
clear and bright, pale yellow-brown in colour, and with no visible sign of foreign matter
or turbidity due to the presence of moisture. Packaging options for turpentine and rosin
are described below, but more detailed packaging and labelling requirements are given in
Appendix 4.

The materials used for the
construction of the plant are important. The dump vat is concrete or mild steel and the
blow-case is mild steel. In order to avoid corrosion by the acidic material, any area
where hot resin is handled should be stainless steel; the melter, filter (where it comes
into contact with the resin), charge tank, still and all pipework are all therefore made
of stainless steel. The wash tank may be aluminium or stainless steel. The condenser,
separator and dehydrator are also usually of stainless steel.

In the United States, melter
capacity varied between 2.5 and 5 tonnes of resin when there were a number of independent
processors. There were usually two or more wash tanks, each capable of holding up to 22
tonnes of resin and each providing material for four distillations. Operation of two
stills, or double shifts, allowed up to 10000 tonnes of resin to be processed in a year.

The scheme of processing followed in
Portugal is based on the same principles which led to the development of the Olustee
process in the United States but some of the units which make up the plant differ in
design and capacity. The process lay-out is illustrated diagrammatically in Figure 3.

Metal drums containing resin are
unloaded at the dump vat. To facilitate the emptying of the drums (which is the most
labour-intensive part of the whole process), a rectangular section (measuring about 25 cm
x 15 cm) is cut out of the side before use. The section is then replaced but can easily be
removed subsequently as required. On receipt, the drums are rolled on their sides to the
vat opening and the resin is forced out with large spatulas. Resin from the dump vat is
fed directly into a mixer (the equivalent of the melter in the previous scheme) with no
intermediate transfer to and from a blow-case. The mixer, rather than being just a
containing vessel like the melter, incorporates a stirrer so that the contents, including
the added turpentine and oxalic acid (if used), can be thoroughly mixed as well as heated.

Another significant difference is
the addition of washing water in the form of live steam (up to 10%) at this stage rather
than in liquid form at a later stage. The hot mixture is next passed through a metal
screen to take out the larger solid impurities; this occurs in a separate vessel rather
than at the bottom of the melter as in the Olustee process.

Figure 3. Scheme of resin
processing in Portugal

Source: Based on Gama (1982)

A slurry of diatomacaeous earth is
added from another vessel and the screened mixture then passes immediately through a fine
filter as before. The hot, filtered mixture passes to one of several decanters in which
the aqueous portion is allowed to settle out, usually overnight; one charge from the mixer
is sufficient to fill one decanter (unlike the Olustee system where one wash tank takes
four to seven charges from the melter).

Both batch and continuous
distillations are carried out in Portugal and although batch stills are predominant, the
larger throughput which is possible with continuous distillation means that a significant
proportion of Portuguese production is obtained in this way. Batch stills in Portugal are
relatively small, with a capacity of 0.5 or 1 tonne, and distillation times are short,
about 20-30 minutes. On completion of the distillation, the rosin is often drained from
the still into a wagon; this can then be pushed between two lines of steel drums spaced
out on a concrete floor, and rosin can be discharged into them by lowering an overflow
arm. Alternatively, paper sacks may be filled.

Stainless steel is again the main
construction material. Mixer and decanter capacities are each about 5-7 tonnes, and there
are usually at least four decanters to provide a constant supply of material for
distillation. Nominal plant capacities range from a few thousand tonnes up to about 10000
tonnes/year.

The target production is determined
by the availability of crude resin, the throughput which can be sustained, and the size of
the market for the products. In some cases, the resin supply may be limited by the number
of suitable trees available for tapping. The annual production capacity required to meet
the target is largely dictated by the still size, the number of stills, and the shifts
worked. The smallest sized plant might have a single still with a capacity of one tonne
and be capable of performing three distillations per day (single shift). The number of
working days available each year will be governed by the length of the tapping season, but
assuming a 260-day year, an annual throughput of around 800 tonnes of resin could be
achieved.

The factors to be considered when
choosing between the different processing systems include relative plant costs,
availability and cost of technical expertise, the costs of maintenance and spare parts,
steam and water requirements, and the relative advantages or disadvantages of using larger
or smaller batch sizes. Estimates of plant costs are discussed in Chapter 4. Data
necessary to make an accurate comparison of steam and water requirements for the different
types of plant are not available. The use of larger stills means fewer distillations are
needed to process a given amount of resin. However, a small still allows for greater
flexibility if interruptions in steam, water or raw material supplies are anticipated. As
the stills designed for distillation of pine resin are not suitable for distilling
harvested plant material to produce essential oils, this is not an option for using spare
capacity should it occur. In any case, the risk of cross-contamination and taints would be
too high.

The labour requirements are
comparatively small for a plant capable of handling up to 1000 tonnes/year of resin. Only
four or five skilled workers and a greater number of general labourers are needed; one
person is normally responsible for operating the still, two or three others assist and
operate the other pieces of equipment, and one is in charge of the boiler. The emptying of
the barrels or drums of crude resin is the most labour-intensive and time-consuming part
of the whole processing operation and at least six labourers are required for unloading,
loading and similar work. A storeman, and office and transport staff, are also required.
The total labour requirements for a larger plant do not increase proportionately as the
same number of workers are needed to operate the specialized pieces of equipment. More
general labourers will be required, though, to handle the greater quantities of resin and
its products.